Camshaft adjusters are used in internal combustion engines to vary the control times of the combustion chamber valves in order to be able to variably configure the phase relationship between a crankshaft and a camshaft in a defined angle range, between a maximum early and a maximum late position. The adjustment of the control times to the current load and rotational speed reduces fuel consumption and emissions. For this purpose, camshaft adjusters are integrated in a drivetrain via which a torque is transmitted by the crankshaft to the camshaft. This drivetrain can be formed, for example, as a belt, chain or gear drive.
In the case of a hydraulic camshaft adjuster, the drive output element and the drive input element form one or more pairs of pressure chambers which act counter to one another and on which hydraulic medium can act. The drive input element and the drive output element are arranged coaxially. A relative movement between the drive input element and the drive output element is generated by filling and emptying individual pressure chambers. The spring which acts rotationally between the drive input element and the drive output element pushes the drive input element in an advantageous direction with respect to the drive output element. This advantageous direction can be in the same direction or in an opposite direction to the direction of rotation.
One design of the hydraulic camshaft adjuster is the vane-cell adjuster. The vane-cell adjuster has a stator, a rotor and a drive input wheel with an external toothing. The rotor is formed as a drive output element so that it can usually be connected in a rotationally fixed manner to the camshaft. The drive input element contains the stator and the drive input wheel. The stator and the drive input wheel are connected to one another in a rotationally conjoint manner or are alternatively formed in one piece with one another. The rotor is arranged coaxially with respect to the stator and within the stator. The rotor and the stator are formed with their radially extending vanes, oppositely acting oil chambers, which can be acted upon by oil pressure and enable a relative rotation between the stator and the rotor. The vanes are formed either in one piece with the rotor or the stator or arranged as a “connected vane” in grooves provided for this purpose of the rotor or the stator. The vane adjusters furthermore have various sealing covers. The stator and the sealing covers are secured to one another by means of several screw connections.
Another design of the hydraulic camshaft adjuster is the axial piston adjuster. In this case, a displacement element is axially displaced by means of oil pressure, which displacement element generates by means of helical gearings a relative rotation between a drive input element and a drive output element.
The control valves of the hydraulic camshaft adjuster control the flow of hydraulic medium between the camshaft adjuster and the oil pump or the oil reservoir (tank).
The control valve has a hollow cylindrical housing and a rotationally symmetrical control piston. The control piston is arranged within the housing of the control valve. The control piston is movable in the axial direction and is guided by the housing. The control piston can thus be positioned in any desired axial position with respect to the housing. The positioning is carried out by an electromagnet which, with its actuating pin, contacts one end of the control piston and can displace the control piston. A spring ensures contact between the control piston and the actuating pin. As a result of the axial positioning of the control piston, the various connections of the control valve are hydraulically connected to one another or separated from one another and can thus communicate with one another or not. Control pistons and housings with openings, e.g. grooves and/or bores, are provided between the connections in order to conduct the hydraulic medium. The control piston has control edges which, together with the edges of the openings of the housing, control the flow rate. The control edges themselves are the edges of the respective opening, e.g. grooves, of the control piston. In order to control the flow rate, the edges of the openings of the housing and the control edges are positioned in relation to one another in such a manner that an opening of the housing is as far as possible opposite an opening of the control piston and forms a flow-through surface for the hydraulic medium which is variable via the capacity to axially position the control piston.
A control valve formed as a central valve is arranged coaxially with respect to the axis of symmetry or rotation of the camshaft adjuster or the camshaft. The central valve is additionally placed within the camshaft adjuster, i.e. the central valve and camshaft adjuster are constructed in a radial direction to one another. The camshaft can optionally be arranged between the camshaft adjuster and the central valve. The housing of the central valve can be formed as a central screw, by which the camshaft adjuster is connected in a rotationally fixed manner to the camshaft. The electromagnet is arranged as a central magnet as far as possible flush with the central valve and is normally arranged fixed on the frame, in particular on the cylinder head.
Alternatively, a control valve with an electromagnet arranged fixedly thereon can be arranged at any desired position in the hydraulic medium gallery, outside the camshaft adjuster and the camshaft, and can control the flow of hydraulic medium.
WO 2010/015541 A1 shows a camshaft adjuster with a central valve. The central valve has two intake connections, wherein one is arranged coaxially with respect to the central valve and the other is arranged radially with respect to the central valve. The intake connections are formed as bores. The central bore furthermore possesses two working connections on the outer circumference which are opposite the hydraulic medium channels to the pressure chambers. The tank connection is arranged on the side which faces away from the camshaft in order to supply hydraulic medium to be displaced into the reservoir of the internal combustion engine.
DE 198 17 319 A1 shows a central valve of a camshaft adjuster. The intake connection is arranged on the outer circumference of the central valve. The intake connection is flanked in the axial direction by both working connections. The tank connection is located on that end of the central valve which faces towards the camshaft and opens into a radial bore of the camshaft.